1. Field of the Invention
The present invention relates to a scan head and an appearance inspection technique, and it particularly relates to a scan head which scans an object under inspection and obtains information, and an appearance inspection method and apparatus which inspect the appearance of the object using the scan head.
2. Description of the Related Art
It is certain that Information Technology (IT) could define an aspect of the new hundreds in the twenty-first century as well as biotechnology. In the IT field, the product cycle is very short as symbolized as xe2x80x9cdog yearxe2x80x9d, and the speed of development and the cost reduction are more critical as ever and a key to the survival of enterprises.
The hardware to support such an IT boom can be categorized into the Internet as an infrastructure, and the information device such as personal computers, personal digital assistance (PDA) and a cellular phone. The latter, that is, various kinds of terminals have been explosively spread and used. It highly owes to downsizing and low price in manufacturing, which has been achieved by high integration design.
High density implementation technology is an element to realize the high integration design, as well as rich types of design tools and advancement in semiconductor technology. The main point in the high density implementation is in manufacturing and inspecting technique. Conventionally, In-Circuit Tester (ICT) has been used to inspect the print circuit board after electrical components are implemented. However, the contact-type inspection apparatus cannot deal with the high density in implementation, and non-contact type, particularly an appearance inspection apparatus using image recognition technique has been highly demanded.
The concept of applying image recognition technology to the appearance inspection is well known for ages. Considering the situation in which even a compact board has several hundreds to over a thousand of parts implemented, however, very high resolution, for example, order of 20 microns, is required for the image to be inspected. Thus it likely takes longer to inspect the board compared to implementing components, and it becomes a very large hamper in a severe competition in product developments.
Under the situations described above, the applicant of the present invention proposed an appearance inspection apparatus having a line sensor in Japanese Patent Application Laid-open No. H8-254500. The apparatus includes a vertical light source as well as a side light source which was common at that time, and switches between two light sources according to testing items. The point of the apparatus is described as follows.
FIG. 1 shows a substrate 1 that is an object under inspection. FIGS. 2A and 2B show the effect of side light 6a and vertical light 6b respectively. As shown in FIG. 2A, when the side light 6a is projected on a component 2, catoptric light 8a reflects sidelong from the horizontal surface of the component 2, but part of the catoptric light 8a reflects vertically upward from the slope where solder 4 is properly mounted. On the other hand, as shown in FIG. 2B, when the vertical light is projected on the component 2, catoptric light 8b reflects totally from the horizontal surface vertically upward, but it is not the case from the slope.
FIGS. 3A and 3B show the images of the substrate 1 under the side light 6a and the vertical light 6b respectively which are captured by a CCD sensor provided above the substrate 1. As shown in FIG. 3A, the image similar to a photograph copy is captured under the side light 6a, and it is comparatively easier to detect a solder bridge across the lead parts of the component, that is, the implementation defect which causes the solder to short-circuit the multiple leads, and a polarity mark on the component which indicates the position and the direction of the component. On the other hand, as shown in FIG. 3B, the high contrast image is captured under the vertical light 6b, and the edge part of the components and the slope part of the soldering appears black. Therefore, it is relatively easier to judge a shift in the location of the components, the absence of the component, and whether solder is properly attached to the electrodes or leads of the component.
As the demand for the appearance inspection apparatus grows increasingly, the inspection speed is still a general problem to be overcome in this field. As a matter of course, the requirement for the accuracy of the image recognition is becoming greater and greater.
The present invention has been made by the applicant in recognition of the above and an object thereof is to provide an appearance inspection technology which is able to meet inherently antinomy in requirements of processing speed and inspection accuracy, and component technology thereof. Another object of the present invention is to further improve the above-mentioned technology proposed by the applicant of the present invention.
An aspect of the present invention relates to a scan head. The scan head for scanning an object under inspection comprises a vertical light source which projects light on a surface of the object from right above, a line sensor which detects catoptric light that reflects vertically upward on the surface, and a lenticular sheet which is inserted between the vertical light source and the object and has a lens surface and a non-lens surface. The lenticular sheet is arranged in a manner such that the lens surface faces to the object and a direction of lens gouges in the lens surface and a scanning direction in the line sensor are nearly orthogonal. Herein, projecting light on the surface of the object from right above means projecting light at an almost zero incident angle onto the surface under inspection. The catoptric light that reflects vertically upward on the surface means light reflected at an almost zero reflection angle from the surface. Namely, the vertical light and the catoptric light pass along almost the same optical axis. Note that strictly speaking, the words of vertical light strictly means the light projected at a zero incident angle, but in this specification the vertical light may have a width from the zero incident angle at a certain degree according to the actual situation of the apparatus.
For instance, the vertical light source may be in a one-dimensional shape and placed in parallel to the line sensor. The line sensor may be a CCD sensor or any other image capturing sensors. The scanning direction in the line sensor means the direction along the long side of the sensor and it is generally orthogonal to the direction of the relative movement of the sensor and the surface under inspection. In the following, the direction of the relative movement is also referred to as a driving direction in this specification and it is discriminated from the scanning direction. The lens used in the lenticular sheet may be in general a cylindrical lens, but any equivalent thereof can be used as long as it has a similar effect in the present invention.
In this aspect of the present invention, it is possible that the light from the vertical light source refracts in the lens surface of the lenticular sheet and the light component vertical to the surface under inspection is stronger than other components. Consequently, the inspection under the vertical light can be performed more accurately.
The lenticular sheet may have a shade material with a line shape attached to the non-lens surface, the shade material being in a position at an opposite side corresponding to each of the lens gouges. In this case, as described later, the lenticular sheet works in a manner such that it can block off light components other than the light vertical to the surface under inspection. Therefore it can contribute to the improvement in the inspection accuracy under the vertical light.
Another aspect of the present invention also relates to a scan head. The scan head has a different configuration in the non-lens surface. Namely, the non-lens surface has a shade material which functions as a slit for incident light to restrain a diffusion of light projected on the object. The same effect stated above can be obtained in this case.
Still another aspect of the present invention also relates to a scan head. In this aspect of the present invention, the lenticular sheet has a lens structure on both surfaces. The main lens surface is configured in a manner such that the main lens surface faces to the object and a direction of lens gouges in the main lens surface and a scanning direction in the line sensor are nearly orthogonal. On the other hand, the sub lens surface faces to the vertical light source and is so configured that each of lens forming the sub lens surface is in a position at an opposite side corresponding to each of lens forming the main lens surface. Furthermore, the sub lens surface has a shade material with a line shape attached to a lens boundary at an opposite side corresponding to each of the lens gouges in the main lens surface. According to this configuration, the above-mentioned effect further increases in general, as described later in an embodiment.
Still another aspect of the present invention relates to an appearance inspection apparatus. The apparatus comprises a scan head which scans the object, and a main unit which synthetically controls the apparatus including the scan head. The scan head includes a vertical light source, and a line sensor which detects catoptric light that reflects vertically upward on the surface and generates image data; and a lenticular sheet stated above or similar. On the other hand, the main unit includes a head control unit which controls a relative movement of the scan head and the object, and an analysis unit which judges on pass or failure for each of test items by examining the image data with predefined judgment criteria. According to this apparatus, a test using the vertical light, as also simply referred to as a vertical light test, can be performed effectively.
Still another aspect of the present invention relates to a scan head. The scan head comprises a line sensor which detects catoptric light that reflects vertically upward on a surface of the object, a vertical light source which is arranged with a predefined width vertically right above the surface along a scanning direction in the line sensor, and a side light source which is arranged sidelong above the surface along the scanning direction in the line sensor. The vertical light source is so configured that a first zone that passes through a central part of the width and a second zone excluding the first zone are enabled to turn on independently. According to this configuration, it is possible that only the first zone or both of the first and the second zone are turned on in a vertical light test, while the second zone is turned on as auxiliary light in a test using the side light, which is also simply referred to as a side light test.
The first zone may be an ideal region in a vertical light test where an intension of the catoptric light by lighting from the first zone is within close to maximum. The image to be obtained under the vertical light is an image by the catoptric light with high contrast. Since the line sensor is arranged in such a manner that it can detect catoptric light that reflects vertically upward on the surface under inspection, if the vertical light is also projected from vertically upward, an image with high contrast can be obtained. However, since the vertical light source has a width herein, although such a phenomenon appears under the projected light from the center, it is a phenomenon close to one under a side light that may be seen under the projected light from the edge. Therefore, the central part by which an image can be detected with high contrast is defined as the first zone, that is, the ideal region in the vertical light test. Thus conversely such a use arises that the second zone is turned on in the side light test to enhance the side light.
Further still another aspect of the present invention relates to an appearance inspection method. The method comprises selecting a first test mode, projecting vertical light on a surface of the object from a vertical light source which is arranged vertically right above the surface and scanning the surface line by line, detecting catoptric light that reflects vertically upward on the surface and generating image data of the surface line by line during the scanning in the first test mode, selecting a second test mode, projecting simultaneously side light from a side light source which is arranged sidelong above the surface, and auxiliary light provided by turning on a zone excluding a central part of the vertical light source and scanning the surface line by line in the second test mode, and detecting catoptric light that reflects vertically upward on the surface and generating image data of the surface line by line during the scanning in the second test mode.
For instance, the first test mode is the vertical light test, and the second test mode is the side light test. According to this aspect of the present invention, the accuracy in the side light test can increase under the auxiliary light. Furthermore, since the part of the vertical light source also serves as a source of the auxiliary light, cost merit and implementation merit can be obtained.
Moreover, any arbitrary combination of the above-mentioned structural components in the present invention is still effective as an embodiment when applied as a method, a system, and a computer program, and so forth.
Moreover, this summary of the invention does not necessarily describe all necessarily features so that the invention may also be sub-combination of these described features.